Machines of this type are often used for the manufacture of eye glasses, in particular for the socalled prescription manufacture, in which lenses are manufactured to order with a specific refractive power. In the case of toric surfaces, two radii must be maintained, namely, the first being the radius of the socalled base curve and the second being the radius of the socalled transverse curve. The base curve is determined in machines of the mentioned type by the length of the swivel arm and the transverse curve by the inclined position of the cup wheel. It is particularly important for the prescription manufacture that the two settings can be carried out quickly and precisely.
In a known machine of the abovementioned type (German AS No. 1 252 555), the first holder is on a swivel arm which projects cantilevered from a swivel bearing. A carriage is movable relative to the swivel axis on the swivel arm, which swivel axis carries an electric motor, on the shaft of which is coupled the cup tool. The second holder is movable in a carriage guide, which is shorter than the carriage, so that same can project beyond the guide. The considerable weight of the movable machine parts effect, depending on the adjustment position, various deformations, which leads to manufacture inexactnesses.
In order to avoid manufacture inexactnesses which are based on such deformations, a machine has also been produced (German Patent No. 22 52 498), in which the workpiece holder is movable on a straight guide and can be lifted and lowered at a right angle with respect to the guide, while the tool holder carries out only pivoting movements. A coordinating of the three movements occurs with the help of exchangeable control cams, which are scanned with sensitive feelers to control the pressure-medium supply to hydraulic drive cylinders. For this a considerable expenditure is needed. Also a large number of templates are needed. The machine is therefore expensive.
The basic purpose of the invention is to provide a machine of the abovementioned type wherein the machine parts are supported such that no deformations occur which are dependent on the respective adjustment position and which unfavorably influence the work result.
The purpose is attained inventively by the first holder being supported through a compound support on the machine frame, whereby the first holder is rotatable in the compound support and has a swivel arm which is connected fixed against rotation to it and along which a swivel-arm bearing is movable. The swivel-arm bearing consists of a swivel-arm holder which is rotatable relative to the machine frame together with the swivel arm and can be locked on same and of a swivel-arm bearing block which is nonrotatable relative to the machine frame, however, is movable in same and lockable on same.
In a so constructed machine, the swivel arm is not loaded by the weight of those parts which are connected to the swivel arm; this weight rather is transmitted through the compound support onto the machine frame. The swivel arm serves only as a guide plate which guides the first holder on the desired circular path. Deflections of the swivel arm by weight forces are thus completely avoided, so that precise work results are achieved in comparison with machines in which heavy weights effect different deformations at different adjustment positions. Since the movements are purely mechanically controlled, the machine suffices without any control-system expenditure to coordinate the movements. It is therefore extraordinarily simple. The adjustment occurs alone by movement of the swivel-arm bearing and by a corresponding rotation of the second holder. Template sets are therefore not needed. The radii can be changed in any desired small steps, which is advantageous in comparison to a machine which needs a separate template for each radius.
The swivel arm is structurally particularly simple and is located below the compound support in a housinglike constructed machine frame. The space below the machine is hereby utilized. The machine must have a certain construction height anyway in order to provide a comfortable working.
A particular locking mechanism has the advantage that adjusting operations are made easier, since the locking mechanism, without a careful adjusting according to scales, assures that the two guides, along which the swivel bearing must be moved, lie exactly parallel to one another. The locking mechanism can be constructed differently, such as by using pressure plates movable into and out of engagement with other components. The swivel bearing is moved preferably by means of a spindle which is arranged in the housing. Such a spindle can both be driven manually and also by means of an electric motor. The respective position of the swivel bearing can for example be indicated by means of a counter, which indicates the rotations of the adjusting spindle.
In order for the effective length of the swivel arm to be able to change, a locking is created between the swivel bearing and the swivel arm. A particularly advantageous embodiment, which can be operated by compressed air, can be utilized. A remote operation is comfortably possible with such a means. However, it is also conceivable to carry out the locking directly by hand. The swivel drive for the first holder can be done manually by a suitable movement on the compound support. This is easily practical, since the rough grinding of the lens, which rough grinding is to be created with the machine, is carried out generally in one single pass. However, a drive by a motor is preferred.
According to a further development of the invention, the second holder has a bearing ring which rests on the machine frame and which encircles the compound support. Through this the second holder is supported very strongly on the machine frame. Upon rotation of the bearing ring for the purpose of adjustment of the transverse curve, the weight stresses do not change, so that also no different deformation at different adjustment positions occur. It is advantageous to provide a mechanism on the bearing ring which can create an air cushion below the bearing ring. With this a rotation of the bearing ring during adjustment operations is made substantially much easier. After removal of the air cushion, the bearing ring due to its heavy weight rests fixedly on the machine frame, so that a further locking is not needed.